Problems with A.N.T. landscape. doesnt edit
What version are you using? Did you add the landscape through Add -> Mesh -> Landscape? Remember that as of blender 2.79, you don't have to install it using a separate file, blender already has it in its optional addons with the compatible version.

For that you can go to user preferences -> add-ons and search for A.N.T and activate it like this:


Ps. I had some trouble when i was first starting out and downloaded the addon from a previous version, causing compatibility problems. 

As described here you could  try:

1 -close blender

2 - rename C:\Users\yournamehere\AppData\Roaming\Blender Foundation\Blender\2.79 
  to
   C:\Users\yournamehere\AppData\Roaming\Blender Foundation\Blender\2.79.bak

start blender, should be good as new now.

Remember to always download from the official blender site, blender.org